Amid the Clatter of Bats, a Call to Feed

Greater mouse-tailed bats live in crowded colonies in caves and also forage in groups, even though the noise from nearby bats can be distracting in using sonar to hunt prey.

Why do they do this? And how do they adjust the distances from one another as they fly? Noam Cvikel and Yossi Yovel of Tel Aviv University set out to answer these questions.

The answer, Dr. Yovel said, is the “bag of chips” effect. It’s probably the crunching sound that attracts the guy in the next cubicle, but for bats, it’s the sonar signal.

When one bat hears another bat hunting, it flies toward the sound, because it signals the presence of food. Of course, if the group gets too crowded, the bats have to spread out because all the echolocation noise makes it hard to hunt.

Dr. Yovel and Mr. Cvikel, and colleagues at Tel Aviv and at the University of Arizona and the University of Maryland, tracked the bats and reported their findings Jan. 8 in Current Biology.

The researchers developed a tiny device that included a GPS-based movement recorder and a microphone. They used surgical glue to attach the devices to greater mouse-tailed bats, recording sounds and movements as the animals hunted at night.

After a few days, the devices fell off and the researchers collected them and analyzed the data. They also played back hunting calls to bats and used computer modeling to see which strategies produced what kind of behavior in the bats.

The scientists examined 1,100 interactions among 12 tagged bats and others, and found that the bats, which can hear others of their kind from more than 100 yards away, were attracted to the particular sound of an attack on prey. “We’re not the first to suggest this,” Dr. Yovel said. But this experiment proved it “robustly.”

The researchers did see a decrease in attacks when the bats got around 10 yards away from other bats, but the strategy of following the hunting noise still seemed successful. The reason, Dr. Yovel said, is that the prey the bats favor, flying queen ants, are hard to find but easy to catch.

“Many people in the past suggested bats interfere with other bats’ sonar,” he said. But he and his colleagues have not seen this, he said, and reported those findings a month ago.

In human terms, it seems the point is to find the buffet table, not shove the other diners aside.